Background art, not prior art, includes a wet-etching method wherein, after a chemical solution is applied to a film to be processed on a substrate, ultraviolet light irradiates the film through the chemical solution to break the molecular bonds of the film, as described in Japanese Patent Application No. 2003-21566 (FIG. 1).
However in a predetermined atmosphere, an organic coating (e.g., oil) may be formed on the film to be processed before wet etching. Since the organic coating makes the film water-repellent, the contact angle between the chemical solution and the film increases. Thus, the wetting properties of the chemical solution will be lowered. If sufficient wetting properties cannot be obtained, there has been a problem that the chemical solution cannot be coated evenly, and the uniformity of the etching rate within the substrate is deteriorated.
If the contact angle between the chemical solution and the film is large, as described above, the coating of the chemical solution 31 is thick as FIG. 5 shows. In a wet-etching method wherein ultraviolet light irradiates the film on the substrate 5 through the chemical solution 20, the thick chemical solution 31 interferes with the transmission of the ultraviolet light, and the light energy of the ultraviolet light is attenuated in the chemical solution 31. Therefore, there has been a problem that the effect of breaking the molecular bonds of the film to be processed is weakened, and the desired etching rate cannot be achieved.
In wet etching by radiating ultraviolet light in an ambient containing oxygen, if ultraviolet light of a wavelength having a high absorption coefficient in oxygen is used, the light energy of the ultraviolet light is attenuated before the ultraviolet light reaches the film to be processed. In this case also, the effect of breaking the molecular bonds of the film to be processed is weakened, leading to the loss of light energy. In order to solve such a problem, there is a method for wet etching in an inert gas, such as nitrogen (N2), to lower the oxygen content to a predetermined value or below. However, to realize this method, there has been a problem of increased equipment costs because of the necessity to provide the etching apparatus with a sealing mechanism 32 as FIG. 6 shows, and increased operation costs due to the wasteful consumption of the inert gas. Also since the displacement of atmosphere in the sealing mechanism 32 is necessary, there has been a problem of requiring a long treatment time, and a lowered throughput.